1. Field of the Invention
The present invention relates to a side curtain air bag which is designed to protect a head of an occupant inside a vehicle by being expanded and developed during lateral collisions or turnover accidents, and to prevent the occupant from being thrown out of the vehicle.
2. Description of Related Art
In existing side curtain air bags, a side curtain air bag module 100, as shown in FIG. 8, is attached along a roof side rail 101 inside a vehicle. At the time of a collision, as shown in FIG. 9, an air bag 103 included in the side curtain air bag module 100 expands and develops into a curtain shape between an occupant and a side component in a vehicle, such as a door, by gas supplied from a gas generator 102, so as to protect the occupant from the side component.
The air bag 103 starts to expand and develop at the initial stage of the collision and comes into protective contact with the head of the occupant. Therefore, when the air bag expands, if the expansive force of the air bag 103 is excessively high and makes the air bag 103 too hard, the expansive force may harm rather than protect the occupant. Accordingly, the expansive force of the air bag is preferred to be relatively low and soft at the initial stage of the collision, when the air bag expands and develops.
In the meantime, at the latter stage of the collision, in order to prevent an occupant from being thrown out the vehicle if it overturns during the collision, the air bag 103 needs to have a relatively high tension. This is necessary to maintain an expanded position along a full forward and backward direction in a curtain shape, to prevent the occupant from being thrown out of the vehicle. For this reason, a tether 104 is attached to the leading and trailing sides below the air bag 103 to keep the air bag 103 in the expanded position. One end of the tether 104 is attached to the air bag 103, and the other end thereof is attached to a chassis.
However, in the related art air bag 103 the tension set by the tether 104 is high as soon as the air bag starts to expand and develop. Therefore, in the prior art it is difficult to make the tension across the air bag low when the air bag initially starts to expand and develop, and become high when the air bag is developed.
In view of the above, it is apparent that there exists a need for an air bag which is capable of controlling the tension across the air bag during initial expansion and after full expansion.